NMR spectrometers for the generation of spectral data typically employ superconducting solenoid magnets to produce a strong vertically oriented static magnetic field B0. The solenoid coils are mounted in a Dewar that provides a low temperature environment required for superconductivity. The Dewar includes a reentrant central tube section that permits the probe to be at a different temperature, usually at room temperature. During the operation of obtaining data, the NMR sample is situated within a probe that contains one or more radio frequency (RF) coils for generating RF magnetic fields that are perpendicular to the static field, B0. The sample is mounted in a sample holder that often also serves as a spinner to rapidly rotate the sample during the time data is being recorded. The probe is connected electrically to the spectrometer console that contains the electronics for generating the RF signals and detecting and recording the NMR response of the nuclei being studied. Provision may also be provided for spinning the sample. This is normally achieved by making the sample holder also serve as a rotor of a gas driven turbine.
When sufficient data has been obtained, the sample holder and sample are ejected from the probe to the top of the Dewar for easy sample exchange. Typically this is achieved by a flow of compressed gas that lifts the sample holder and sample through a cylindrical pipe to the exchange region at the top of the Dewar where it can be easily removed and if desired exchanged with the next sample to be analyzed. The gas flow must be maintained until the operator removes the sample and possibly replaces it by the next sample to be analyzed. When inserting the next sample, the gas flow must be maintained until it is ready to be inserted into the probe. If the gas flow should fail during any of these steps, the sample and sample holder would drop prematurely and in an uncontrolled fashion into the magnet.